HVAC controllers are used widely in dwellings, buildings, and other controlled spaces. In many cases, the HVAC controllers are mounted on a wall or the like to allow for the measurement and control of the temperature, humidity and/or other environmental parameter within the space. HVAC controllers come in a variety of shapes and with a variety of functions. Advanced HVAC controllers have built in electronics, often with solid state sensors, to sense and control various environmental parameters within a space. The user interface of some electronic HVAC controllers includes software controlled buttons and/or a display.
HVAC controllers often utilize a battery power source as a main power source and/or back-up power source. As a back-up power source, batteries are often used to retain the programmed parameters in the event that the normal power source in the controller circuit is removed or becomes ineffective. In some controllers, both such features are provided by a battery (or several batteries) mounted within the controller. A battery also helps maintain real time in the event of a power interruption.
A battery, however, has certain disadvantages. For example, it requires mounting space, sometimes a significant amount, within the controller. Also, the battery should be replaced periodically. Such replacement is an inconvenience to the user as it often requires dismantling at least a portion of the controller and proper replacement and re-assembly.